There are a LOT of folks who say you MUST have one or you'll burn out your gauge. That's not my experience. When I converted my 55.1 panel from 6v to 12v years ago I didn't put a reducer on any of the gauges (never thought about needing to). I put over 100K on the panel after the conversion without a single problem with any of the gauges. Maybe I was just lucky or maybe it's not really necessary. I don't know, just advising of my personal experience.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.